System and methods for mixed-signal computing

ABSTRACT

Systems and methods of implementing a mixed-signal integrated circuit includes sourcing, by a reference signal source, a plurality of analog reference signals along a shared signal communication path to a plurality of local accumulators; producing an electrical charge, at each of the plurality of local accumulators, based on each of the plurality of analog reference signals; adding or subtracting, by each of the plurality of local accumulators, the electrical charge to an energy storage device of each of the plurality of local accumulators over a predetermined period; summing along the shared communication path the electrical charge from the energy storage device of each of the plurality of local accumulators at an end of the predetermined period; and generating an output based on a sum of the electrical charge from each of the plurality of local accumulators.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/280,317, filed 20 Feb. 2019, which is a continuation of U.S. Pat. No.10,255,205, issued 9 Apr. 2019, which claims the benefit of U.S.Provisional Application No. 62/559,354, filed 15 Sep. 2017, which areincorporated in their entireties by this reference.

TECHNICAL FIELD

The inventions herein relate generally to the integrated circuitryarchitecture field, and more specifically to new and useful mixed-signalintegrated circuits and methods of computing mixed-signals in theintegrated circuitry architecture field.

BACKGROUND

Today, the various implementations of artificial intelligence aredriving innovation in many fields of technology. Artificial intelligence(AI) systems and artificial intelligence models (including algorithms)are defined by many system architectures and models that enable machinelearning (deep learning), reasoning, inferential capacities, and largedata processing capabilities of a machine (e.g., a computer and/or acomputing server). These AI systems and models are often trainedintensively to perform one or more specific tasks, such as naturallanguage processing, image recognition, planning, decision-making, andthe like. For example, a subset of these AI systems and models includeartificial neural network models. The training of an artificial neuralnetwork model may, in many cases, require thousands of hours across thetraining cycle and many terabytes of training data to fine tuneassociated neural network algorithm(s) of the model before use.

However, once trained, a neural network model or algorithm may bedeployed quickly to make inferences to accomplish specific tasks (e.g.,recognizing speech from speech input data, etc.) based on relativelysmaller datasets when compared to the larger training datasets usedduring the training cycle. The inferences made by the neural networkmodel or algorithm based on the smaller datasets may be a predictionabout what the neural network calculates to be a correct answer orindication about a circumstance.

Still, while neural network models or algorithms may not require a sameamount of compute resources, as required in a training phase, deployinga neural network model or algorithm in the field continues to requiresignificant circuitry area, energy, and compute power to classify dataand infer or predict a result. This is because many of the traditionalcomputers and systems that implement neural network models or algorithmstend to be larger to accommodate a great amount of circuitry needed forcomputing power and increased data processing speeds when implementingthe neural network model and due to the large size of the circuitry,more energy is required to enable the compute power of the manycircuits.

These traditional computers and systems for implementing artificialintelligence models and, namely, neural network models may be suitablefor remote computing, such as in distributed computing systems (e.g.,the cloud), or when using many onsite computing servers and the like.However, latency problems are manifest when these remote artificialintelligence processing systems are used in computing inferences and thelike for remote, edge computing devices or in field devices. That is,when these traditional remote systems seek to implement a neural networkmodel for generating inferences to be used in remote field devices,there are unavoidable delays in receiving input data from the remotefield devices because the input data must often be transmitted over anetwork with varying bandwidth and subsequently, inferences generated bythe remote computing system must be transmitted back to the remote fielddevices via a same or similar network.

Implementing AI processing systems at the field level (e.g., locally atthe remote field device) may be a proposed solution to resolve some ofthe latency issues. However, attempts to implement some of thesetraditional AI computers and systems at an edge device (e.g. remotefield device) may result in a bulky system with many circuits, asmentioned above, that consumes significant amounts of energy due to therequired complex architecture of the computing system used in processingdata and generating inferences. Thus, such a proposal without more maynot be feasible and/or sustainable with current technology.

Accordingly, there is a need for a deployable system for implementingartificial intelligence models locally in the field (e.g., local AI),and preferably to be used in edge devices, that do not result in large,bulky (edge) devices, that reduces latency, and that have necessarycompute power to make predictions or inferences, in real-time orsubstantially real-time, while also being energy efficient.

The below-described embodiments of the present application provide suchadvanced and improved integrated circuits and implementation techniquescapable of addressing the deficiencies of traditional systems andintegrated circuit architectures for implementing AI and machinelearning.

SUMMARY OF THE INVENTION

In one embodiment, a mixed-signal integrated circuit includes areference signal source that generates a plurality of analog referencesignals based on digital input, wherein an output terminal of thereference signal source is electrically connected to a shared signalpath, and wherein the reference signal source sources the plurality ofanalog reference signals to the shared signal path; a plurality of localsignal accumulators arranged along the shared signal path and each ofthe plurality of local signal accumulators having an input terminalelectrically connected to the shared signal path, wherein each of theplurality of local signal accumulators: collects, via the shared signalpath, the plurality of analog reference signals from the referencesignal source; and stores a sum of the plurality of electrical chargesover a predetermined number of clock cycles.

In one embodiment, each of the plurality of local signal accumulatorsfurther: receives one or more biasing signal input or control signalinput for incrementing or decrementing each of the plurality ofelectrical charges to an energy storage device.

In one embodiment, an output terminal of each of the plurality of localsignal accumulators is electrically connected to one input terminal of aplurality of input terminals of a neural network implementation, andeach of the plurality of local signal accumulators outputs the sum ofthe plurality of electrical charges to one input terminal of theplurality of input terminals of the neural network implementation.

In one embodiment, each of a plurality of output terminals of the neuralnetwork implementation is electrically connected to an input terminal ofeach of a plurality of local analog-to-digital converters, and each ofthe plurality of output terminals of the neural network implementationsources an analog output signal to an internal node of each of theplurality of local analog-to-digital converters.

In one embodiment, an output terminal of each of the plurality of localsignal accumulators is electrically connected to an input terminal ofthe internal node of each of the plurality of local analog-to-digitalconverters, and each of the plurality of local analog-to-digitalconverters outputs a binary biasing signal to a respective one of theplurality of local signal accumulators for incrementing or decrementingeach of the plurality of electrical charges to an energy storage device.

In one embodiment, each of the plurality of local accumulators comprisesa digital-to-analog converter comprising: a pair of current mirrors thatduplicate a plurality of current charges generated based on theplurality of analog reference signals provided via the shared signalpath; and an energy storage device that stores the sum of the pluralityof electrical charges.

In one embodiment, each of the plurality of local accumulators comprisesa digital-to-analog converters comprising: an energy storage device; andan amplifier that integrates the plurality of electrical charges overconsecutive clock cycles on the energy storage device.

In one embodiment, the reference signal source comprises abinary-weighted digital-to-analog converter that generatesbinary-weighted analog reference signals, the plurality of analogreference signals comprise a plurality of binary-weighted analogreference signals that vary in value over the predetermined number ofclock cycles, and each of the plurality of local accumulators sums theplurality of electrical charges on an energy storage device based on theplurality of binary-weighted analog reference signals for each clockcycle of the predetermined number of clock cycles.

In one embodiment, the reference signal source comprises an N-bitbinary-weighted digital-to-analog converter, where N represents a numberof bits, wherein the predetermined number of clock cycles equals N clockcycles, and each of the plurality of local accumulators sum theplurality of electrical charges over N clock cycles.

In one embodiment, each of the plurality of local accumulators comprisesa programmable current source that generates an electrical currentcharge based on each of the plurality of analog reference signals.

In one embodiment, the reference signal source comprises a single globaldigital-to-analog converter that includes circuitry that generates theplurality of analog reference signals; and the plurality localaccumulators comprise a plurality of local digital-to-analog convertershaving circuitry distinct from the circuitry of the single globaldigital-to-analog converter.

In one embodiment, the reference signal source comprises a thermometerencoding global digital-to-analog converter that generates thermometerencoded analog reference signals, wherein the plurality of analogreference signals comprise a plurality of thermometer encoded analogreference signals having a constant value; and each of the plurality oflocal accumulators stores the sum of the plurality of electrical chargeson an energy storage device based on the plurality of thermometerencoded analog reference signals for each clock cycle of thepredetermined number of clock cycles.

In one embodiment, the reference signal source comprises a segmentedglobal signal reference source comprising two or more signal referencesources that are combined and generate high resolution analog referencesignals, wherein the plurality of analog reference signals comprise aplurality of high resolution analog reference signals, and each of theplurality of local accumulators stores the sum of the plurality ofelectrical on an energy storage device based on the plurality of highresolution analog reference signals for each clock cycle of thepredetermined number of clock cycles.

In one embodiment, the shared signal path comprises a singleelectrically conductive signal wire having multiple connections thatconnect each of the plurality of local accumulators at distinctpositions along the shared signal path.

In one embodiment, the plurality of analog reference signals generatedby the reference source comprise a plurality of voltage referencesignals, and each of the plurality of local accumulators converts theplurality of voltage reference signals to a plurality of currentcharges.

In one embodiment, the reference signal source comprises a currentsource global digital-to-analog converter that generates a currentreference signal based on a selection of one current source of aplurality of current sources, wherein the plurality of analog referencesignals comprise a plurality of current reference signals; and each ofthe plurality of local accumulators stores the sum of the plurality ofelectrical charges on an energy storage device based on the plurality ofcurrent reference signals for each clock cycle of the predeterminednumber of clock cycles.

In one embodiment, a method of implementing a mixed-signal computingcircuit includes sourcing, by a global reference signal source, aplurality of analog reference signals along a shared signalcommunication path to a plurality of local accumulators; producing aplurality of electrical charges, at each of the plurality of localaccumulators, based on the plurality of analog reference signals; addingor subtracting, by each of the plurality of local accumulators, each ofthe plurality of electrical charges to an energy storage deviceassociated with each of the plurality of local accumulators over apredetermined period; and generating, by each of the plurality of localaccumulators, an output based on a sum of the plurality of electricalcharges.

In one embodiment, the shared signal path comprises a singleelectrically conductive signal wire having multiple connections thatconnect an input terminal of each of the plurality of local accumulatorsat distinct positions along the shared signal path, and each of theplurality of local accumulators being serially arranged along the sharedsignal path downstream of the global reference source.

In one embodiment, an output terminal of each of the plurality of localsignal accumulators is electrically connected to one input terminal of aplurality of input terminals of a neural network implementation, andeach of the plurality of local signal accumulators outputs the sum ofthe plurality of electrical charges to the one input terminal of theplurality of input terminals of the neural network implementation.

In one embodiment, each of a plurality of output terminals of the neuralnetwork implementation is electrically connected to an input terminal ofeach of a plurality of local analog-to-digital converters, each of theplurality of output terminals of the neural network implementationsources an analog output signal to a sub-circuit of each of theplurality of local analog-to-digital converters, and an output terminalof each of the plurality of local signal accumulators is in electricallycommunication with an input terminal of the sub-circuit of each of theplurality of local analog-to-digital converters.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic of an integrated circuit 100 inaccordance with one or more embodiments of the present application;

FIGS. 1A-1B illustrate implementations of one or more portions of thesystem 100 in accordance with one or more embodiments of the presentapplication;

FIG. 2 illustrates a method 200 in accordance with one or moreembodiments of the present application;

FIG. 3 illustrates an implementation of a system for mixed-signalcomputing in accordance with one or more embodiments of the presentapplication;

FIG. 3A illustrates a specific implementation of the system formixed-signal computing of FIG. 3 in accordance with one or moreembodiments of the present application; and

FIG. 4 illustrates a schematic of a subsystem of an integrated circuitin accordance with one or more embodiments of the present application.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of preferred embodiments of the presentapplication are not intended to limit the inventions to these preferredembodiments, but rather to enable any person skilled in the art of tomake and use these inventions.

Overview

In traditional integrated circuits used in implementingcomputationally-intensive programs or applications (e.g., deep neuralnetwork algorithms) and the like, the typical integrated circuit (IC)architecture includes relatively large circuits requiring large area andpower to operate and perform computations. This is because processingdigital signals (e.g., binary signals) often requires large and powerhungry implementations of circuits. Thus, for many technologicalimplementations of computationally-intensive programs, such asartificial intelligence models, the resulting computer ICs having theselarge circuits for processing digital signals are also large andtherefore, less feasible to include in space-constrained edge devicesand the like.

Further, a great majority of the computational effort of an integratedcircuit in implementing computationally-intensive applications, such asneural network models, involve performing thousands to millions ofmatrix multiplications. Further, in digital signal processing for neuralnetwork models, multiply-accumulate operations may also be performed inwhich a product of two numbers is computed and the product then added toan accumulator. Thus, when neural network models are implemented usingonly or primarily digital circuitry, the resulting digital circuitryconsumes large amounts of energy performing the calculations and storingweight coefficients for neurons and resultant products of the manymultiply-accumulate operations.

As a technical solution to reduce power required for computing and anoverall size of an integrated circuit that is capable ofcomputationally-intensive processes includes providing mixed-signalcomputing architectures that may be implemented utilizing extremely areaefficient digital-to-analog converters (DACs) (rather than standard DACswhich are fundamentally large, or area-intensive) along-side the variousother circuitry of an integrated circuit to achieve area and energyefficiencies. However, integrated circuits that may be implemented usingtraditional DACs for computationally-intensive implementations, may mostlikely require a very large number of DACs (e.g., thousands of DACs) toachieve matching and to achieve required speed and noise performances.Therefore, while traditional implementations of DAC architectures may beuseful to reduce energy required by and an overall size of an integratedcircuit, these traditional implementations of DAC architectures may notbe feasible due to the large number of DACs that may be necessary toprocess computationally-intensive AI programs and applications.

The embodiments of the present application, however, solve at least theabove-noted technical problems by implementing, in various forms, aglobal (reference signal source) DAC that is in operable communicationand control of a plurality of local (output) DACs. The embodimentsdescribed herein function to solve a fundamental technical problem withmixed-signal computing architectures by enabling a creation of manyprecise DACs without consuming a very large area on a chip. By contrast,modern DACs implementing computationally-intensive programs and the likemay typically become large due to matching constraints on their variouscomponents, which dictate the lower bound on device size. This technicalproblem becomes further apparent and problematic once the DAC resolutionsurpasses 6-8 bits. Consequently, these traditional DACs may not beenergy or size efficient once noise and speed are considered in theDAC's architecture.

In embodiments of the present application, the global (reference) DACfunctions as a signal source (in some embodiments, the only referencesignal source) to each of the local (mirror) DACs. In a preferredembodiment, the local DACs function to serially accumulate analogreference signals generated by the global DAC over a number of clockcycles. In such embodiment, the accumulation by each of the local DACsis onto a capacitor or other energy storage device for the providing anew or total output (e.g., a charge representing the accumulation of thereference signals).

Accordingly, implementing the global DAC and plurality of local DACs inthe manner described above enables a reduction of a number ofhigh-precision reference devices required for driving the local DACs, aseach local DAC would typically require a respective dedicated referencedevices that provide a reference signal. In traditional DACs, areference signal generation as well as output circuitry may be usuallyintegrated into a single large DAC. Accordingly, in several embodimentsof the present application, the global DAC functions to provide precisesource signaling to each of a plurality of local DACs thereforeameliorating the matching requirement for implementing accurate DACs andmore specifically, a need for a plurality of reference signal sourceDACs to drive a plurality local output DACs (e.g., eliminating 1-to-1match). Accordingly, a reduction in DAC architecture area may beachieved and, computer and power efficiencies that allow edge computingdevices and the like to perform complex and computer-intensiveoperations including AI computing locally at a source of the input data.

1. A System for Mixed-Signal Computing

As shown in FIG. 1 , a system 100 for implementing mixed-signalcomputing for computationally-intensive programs and/or applicationsincludes a global reference generator 110, a plurality of localaccumulators 120, and a shared signal path 125. As shown in FIG. 1A, insome embodiments, the local accumulators 120 may each include an energystorage device 122, and current mirrors 124. Additionally, oralternatively, as shown in FIG. 1B, each of the local accumulators 120may include an energy storage device and an amplifier 126, in someembodiments. The system of 100 may preferably be implemented in a morecomprehensive system, as described in U.S. Provisional Application No.62/694,355, which is incorporated herein by this reference in itsentirety.

The system 100 preferably functions to bifurcate typical functionalityof a digital-to-analog converter into at least two component devices.The first component, in several embodiments, includes the globalreference generator 110 that functions to define or generate one or more(analog) reference signals, such as a current, based on a digital inputinto the global reference generator 110. In some embodiments, the globalreference generator 110 may comprise a binary-weighted global referencegenerator that may be implemented as described in U.S. ProvisionalApplication No. 62/644,908, which is incorporated herein by reference inits entirety. The second component, in several embodiments, includes aset of local accumulating devices that function to receive, via a sharedsignal path 125, the reference signals from the global referencegenerator 110 and further function, in some embodiments, to perform somean integration of the reference signals, such as an arithmetic function(e.g., addition, subtraction, etc.) of the values of the referencesignals over a set period of time (e.g., over a predetermined number ofclock cycles). As with several of the embodiments of the presentapplication, the arithmetic function (e.g., summation) and/orincrementing and decrementing function may be driven by a biasing signalor control input signal received at a local accumulator 120. The biasingsignal or control signal input may be generated by any suitable biasinginput source or control signal input source including a dedicated biasgenerator or bias input source, a control processor, a comparator,and/or by a global reference generator 110.

Additionally, or alternatively, in some embodiments, the system 100 mayfunction to generate and provide differential signaling input to each ofthe plurality of local accumulators 120 for driving output valuestherein. In such embodiments, the system 100 may function toelectrically transmit analog reference signals and/or control inputsignals to each of the plurality of local accumulators via twocomplementary signals, as a differential pair of signals.

The system 100 functions to achieve scale and area efficiency (e.g., tomake a smaller integrated circuit) with, at least, the above-describedconfiguration by allowing the first component to be large and capable ofgenerating accurate reference signals for the second componentcomprising the set of small, local accumulating devices. That is, thearea and power of the first component (which would be matching and noiselimited) is now amortized. Therefore, the system 100 enables anintegrated circuit architecture that is capable of performingcomputationally-intensive operations while having extremely high areaand power efficiencies.

The global reference generator 110 functions to generate referencesignals for each of a plurality of local accumulators 120. The globalreference generator 110 may sometimes be referred to herein as a globalsignal source. Preferably the global reference generator 110 comprises aglobal digital-to-analog converter (DAC), as shown in FIG. 3 . In suchcase, the global DAC may function to receive, as inputs, digital signals(e.g., binary number or input) from an external source, an upstreamlayer, an upstream device, and/or the like and function to output analogreference signals (e.g., a voltage or current signal) to a plurality oflocal DACs. In one or more embodiments in which the global referencegenerator 110 comprises a digital-to-analog converter, the system 100may function to implement any suitable type of kind of digital-to-analogconverter including, but not limited to, a resistor ladder DAC, an R-2Rladder DAC, a current source DAC, a binary-weighted DAC,thermometer-encoded DAC, segmented DAC, a multiplying DAC, a hybrid DAC,and/or the like.

In one or more embodiments, the global source generator 110 comprises asimplified digital-to-analog converter and thus, may not be a fulldigital-to-analog converter that may typically output 256 bits or levelsof analog output. Rather, in one or more preferred embodiments, aconfiguration of the global source generator 110, when implemented as aDAC, may be limited such that the DAC may only output eight levels(i.e., an 8-bit DAC with less current and/or resistance sources). Thesimplified structure and/or configuration of such a global referencegenerator 110, when implemented as a DAC with limited levels of output,enables an implementation of an integrated circuit with a smallerfootprint and correspondingly, lower power usage because of the smallercircuit size. It shall be noted, however, that while in one or moreembodiments it is preferably to use a limited (circuitry) DAC as aglobal reference generator, it may be possible to use any suitableand/or type of DAC of any size and having any number of output levels.

Accordingly, the global DAC may function to source analog referencesignals to the local accumulators (e.g., local DACs) based on digitalinput received at the global DAC. Additionally, or alternatively, thereference signal generated and transmitted by the global referencegenerator 110 to each of the local accumulators may be an analogreference signal, such as a current or voltage, that may be used tocontrol or drive functionality of the local accumulators 120.Accordingly, the global reference signals provided by the globalreference generator 110 are preferably transmitted to the localaccumulators 120 via a shared signal path 125 (e.g., a shared or commonwire) that operably connects the local accumulators 120 to each other aswell as to a same global reference generator 110.

The shared signal path 125 preferably extends from an output terminal ofthe global reference generator 110 downstream to each of a plurality oflocal accumulators that are connected at respective input terminalsthereof. final output circuitry (e.g., an analog-to-digital converter orthe like). Additionally, or alternatively, each of a plurality of localaccumulators 120 may be serially arranged or positioned along the sharedsignal path 125. The shared signal path 125 is preferably connected toan output terminal of the global reference generator 110 and each of theinput terminals of each of the plurality of local accumulators 120.

Referring to FIG. 3 , FIGURE illustrates one implementation of theglobal DAC-to-local DACs architecture in a neural network implementationin which a plurality of local DACs (LDACs) function to receive one ormore analog reference signals from a single global DAC (GDAC) (e.g.,global reference generator no) and resultantly, each of the LDACsgenerates an output to the neural network implementation. In thisimplementation, the output generated by each of the LDACs may bereceived as input into respective input terminals of the neural networkimplementation. The output terminals, in such implementation, of eachrespective LDAC may be electrically connected (directly (e.g., withoutany intervening nodes) or indirectly) to respective input terminals ofthe neural network implementation. Additionally, or alternatively, aplurality of biasing inputs (e.g., A_input, B_input, C_input, etc.) maybe provided to each of the plurality of LDACs that function to steer ordirect an incrementing or decrementing function of each LDAC. Forinstance, in one embodiment, Accordingly, a biasing input source (e.g.,a dedicated biasing input source or a global reference source) localinputs (e.g., A_input, B_input, etc.) to the input terminals of theneural network implementation that may be received at each local DAC maybe applied against a tunable resistor (programmable current source) thatgenerates an amount of current charge. With each column of tunableresistors acting as a neuron column (of a neural network) incombination, the current output generated at each tunable resistor in aneuron column may be aggregated (or summed together), as illustrated inFIG. 3A, to form a single, aggregate current output (e.g., a neuronoutput). Additionally, or alternatively, the aggregate current outputmay be converted to a digital output using an analog-to-digitalconverter or any other suitable output circuitry.

Referring to FIG. 4 , FIG. 4 illustrates another implementation (relatedto the implementations of FIGS. 3-3A) in which output from a neuralnetwork implementation (or any computationally-intensive implementation,any parallel data processing network, and/or any suitable output source)passes as input into an analog-to-digital converter. In one embodimentof this implementation, the neural network implementation may include aplurality of neural network columns that each produce a respectiveneuron output (i.e., neuron column output). In this embodiment, aplurality of local analog-to-digital converters (ADCs) may be arrangedto receive the respective neuron outputs from each respective neuroncolumn of the neural network implementation.

Additionally, or alternatively, each of the plurality of local ADCs 410may be configured or designed with a local DAC 420 and an internal node430. Accordingly, in such implementation, the global DAC-to-local DACsarchitecture may be implemented with the plurality of local ADCs 410such that each of the plurality of local ADCs 410 includes a local DACand each of the input terminals of the local DACs may be arranged alonga shared signal path for receiving one or more reference signals fromthe global DAC 415. In some embodiments, the global DAC 415 may be thesame as the global reference generator 110, such that the referencesignals for the plurality local accumulators 120 and the plurality oflocal DACs 420 originate from a same signal source. It shall be notedthat the internal node 430 of each of the local ADCs may include, butshall not be limited to, a comparator circuit, an amplifier, and/or anysuitable sub-circuit. In one or more preferred embodiments, the internalnode 430 comprises a comparator circuit and the like.

In operation, each of the plurality of local ADCs 410 may function toreceive an analog neuron output from a respective neuron column of theneural network implementation and convert the analog neuron output to adigital (i.e., a binary value). Correspondingly, each of the local DACs420 may function to receive reference signals from the global DAC 415that each of the local DACs 420 may function to source to the internalnode 430 of the local ADC 410. Accordingly, based on a neuron output anda reference signal from a local DAC 420, each respective local ADC 410may function to generate a binary output. In some embodiments, thebinary output generated by each respective local ADC 410 may be abiasing input signal to a respective local DAC 420 of each local ADC 420for incrementing or decrementing a charge on a local capacitor orstorage device associated with the local DAC 420.

Accordingly, in typical digital circuitry used for implementing neuralnetwork models, the matrix multiplication calculations are performedusing digital values (binary values). By comparison, in embodiments ofthe system 100 implementing a mixed-signal computing architecture, thematrix multiplication calculations are performed in the current (analog)domain thereby allowing for up to fifty times (Sox) or greaterimprovement in power consumption by the system. That is, the system 100functions to lower power consumption by up to 50× or greater.

Generally, the global reference generator no may be configured with ahigh-speed analog design with better matching and noise performance.Additionally, or alternatively, the configuration of the globalreference generator 110 may include reference signal generation devicesand/or circuitry that allows the global reference generator 110 togenerate analog reference signals and also, causes the global referencegenerator 110 to be large relative to each of the plurality of localaccumulators 120. Additionally, or alternatively, the global referencegenerator no may be configured to transmit reference signalssequentially (e.g., one at a time) or simultaneously (e.g., multiplesignals per clock cycle). It shall be noted that the global referencegenerator no may be configured to generate and/or transmit referencesignals in any suitable manner contemplated herein or otherwise known inthe art.

The shared signal path 125 may be a single (electrically conductive)signal wire, signal trace, or signal path with multiple connections tothe plurality of local accumulators 120. The shared signal pathpreferably functions to allow a transmission of reference signals fromthe global reference generator no to each of the plurality of localaccumulators 120 that are connected thereto or positioned (or arranged)along the shared signal path 125. The shared signal path 125 may beconfigured such that any reference signal originating from the globalreference generator no being transmitted along the shared signal path125 may be copied or otherwise, mirrored by each of the localaccumulators 120 connected to the shared signal path 125.

In one implementation, the shared signal path 125 may be used by theglobal reference generator no to provide serialized (analog) referencesignals. Accordingly, in such implementation, the shared signal path 125may function to provide single bit reference signals every clock cycleto the local accumulators 120. For instance, if the global referencegenerator 110 comprises a three-bit DAC or the like, the shared signalpath 125 may provide each of the three bits individually andsequentially to each of the plurality of local accumulators 120 andpreferably, in three clock cycles. In this way, the shared signal path125 enables a single signal source (e.g., the global referencegenerator) to provide accurate reference signals to multiple localaccumulators in lieu of a dedicated signal source for each of the localaccumulators 120. A technical benefit of such configuration isconsiderably smaller circuitry for implementingcomputationally-intensive applications and/or programs (e.g., neuralnetwork models, etc.).

The local accumulators 120 may function to generate an analog output toa local output receiver (e.g., local analog-to-digital converter) or thelike, such as illustrated in FIG. 3A. In a preferred embodiment, theplurality of local accumulators 120 comprise a plurality of localdigital-to-analog converters (LDACs) that may function to generate theanalog output over several clock cycles using the global referencesignals from the global reference generator 110. It shall be noted thatdepending on the reference signal generation mode of the globalreference generator 110, the plurality of local accumulators 120 maygenerate the analog output over a single clock cycle. The configurationof the LDACs may generally exclude reference signal generation devices,as the reference signals for each of the LDACs may be provided by theglobal reference generator 110 and in general, the reference signalgeneration devices and/or circuitry are large. Resultantly, thisconfiguration enables the LDACs to be considerably smaller in size andarea consumed on a printed circuit board or panel of an integratedcircuit. In comparison to a global DAC, for instance, the LDACs may beup to ten (10) to twenty (20) or more times smaller in size and area.This allows for great area and power efficiencies on an integratedcircuit or computer chip. However, it shall be noted that, in someembodiments, each of the plurality of LDACs may include one or moretypes of reference signalaccumulation/aggregation/summation/reconstruction circuitry thatfunction to output a resultant reference signal, as discussed in moredetail below. That is, while in some embodiments, the local accumulators120 (or LDACs) may function to accumulate reference signals, it is alsopossible in some variations for the local accumulators toincrement/decrement an energy storage device or perform summationfunctions based on the encoding scheme of the global reference generator110 and the configuration of each respective local accumulator 120.

As mentioned above, each of the plurality of local accumulators 120 mayinclude an energy storage device 122, current mirrors 124, and in someembodiments, comparator circuitry. The energy storage device 122preferably functions to store locally at the local accumulator 120energy values, such as analog energy values including current or voltagevalues. Preferably the energy storage device 122 comprises a capacitor,however, the energy storage device 122 may be any suitable electricalenergy storing element, such as a flash transistor operating in seriesor the like. In some embodiments, each of the plurality of localaccumulators 120 may function to perform arithmetic functions againstthe energy storage device 122 based on one or more signal inputs (e.g.,sequential inputs). Accordingly, a local accumulator 120 may function toadd and/or subtract charge on the energy storage device 122 depending ona value of a received reference signal. Each local accumulator 120 may,additionally or alternatively, function to integrate a (voltage) chargeon the capacitor based on one or more signal inputs.

The current mirrors 124 of each of the plurality of local accumulators120 function to duplicate or copy a reference current signal providedthrough the shared signal path 125. Specifically, in some embodiments,the global reference generator 110 functions to provide a referencecurrent signal via the shared signal path 125. The reference currentsignal may be received by each of the local accumulators 120 connectedto or positioned along the shared signal path 125. Accordingly, usingthe current mirrors 124 at each respective local accumulator 120, thelocal accumulator 120 functions to copy the reference current signal(e.g., the global reference signal) for purposes of generating oraccumulating an output signal.

In a preferred embodiment, the current mirrors 124 comprise circuitsdesigned to copy a current through one active device by controlling thecurrent in another active device of a circuit while keeping the outputcurrent constant irrespective of loading. The current mirrors 124 mayfunction to copy a varying signal current or a constant signal current(depending on whether the global reference generator 110 provides aconstant or varying global reference signal) and provide bias currentsand/or active loads to circuits. Preferably, the circuits defining thecurrent mirrors 124 include an inverting current amplifier (ideally)that, in most embodiments, functions to reverse a current direction aswell or may be a current-controlled current source. However, it shall benoted that the current mirrors may include any suitable circuitry forcopying a reference current signal.

Referring to FIG. 1A, one implementation of a local accumulator 120 isillustrated in which the global reference generator 110 functions togenerate bias voltages (e.g., global reference signals) for two currentmirrors 124 in the local accumulator 120. The bias voltages provided bythe global reference generator 110 may be generated such that thecurrents copied in the current mirrors 124 are weighted. For instance,in a binary-weighted implementation of the global reference generator110 of system 100, bias voltages generated by the global referencegenerator no may be updated every clock cycle. In this way, the copiedcurrent in the current mirrors 124 changes in a binary fashion. In thisimplementation, a sequential input or the like may be added in somecharge on the energy storage device 122 (capacitor) of the localaccumulator 120 or some charged subtracted from the energy storagedevice 122. The amount of charge that is added to or subtracted from theenergy storage device 122 is preferably a function of the copied currentin the local accumulator 120—since the copied current changes in abinary fashion, the charge added or subtracted functions to change in asimilar or same manner. Accordingly, for an N-bit (e.g., 8-bit) globalDAC or the like, N (e.g., N=8) clock cycles would be required to createa required output at the local DAC.

In one variant implementation of the system 100, the local accumulator120 when implemented as a LDAC functions to increment/decrement a chargeon an energy storage device 122 based on thermometer encoded referencesignals provided by the global reference generator 110 (thermometerencoding global reference generator). In such variant implementation, anamount of charge incremented or decremented from the energy storagedevice 122 may be constant in each clock cycle. In such implementation,for an N-bit global reference generator 110, 2{circumflex over ( )}Ncycles would be required to create a required output at the localaccumulator 120 (LDAC).

Additionally, in yet a further implementation, a segmented globalreference generator 110 may be implemented in which two or more globalreference generators (or two or more DACs) are combined to achieve asingle, higher resolution global reference generator 110 to provide arequired performance (e.g., more accurate reference signal generation,better matching, higher noise performance, etc.) and generate highresolution analog reference signals (e.g., analog signals having aresolution and/or accuracy satisfying or exceeding a resolutionthreshold). In use, the different segments of the higher resolutionglobal reference generator may be used to handle various signalgeneration tasks where the outputs of these different segments may becombined to achieve a unitary output. In one or more embodiments inwhich a segmented global reference generator may be implemented using acombination of two binary-weighted DACs that includes eight (8) currentsources. In such embodiments, each of the two binary-weighted DACs mayoutput half of a required current value to each of the integrators orlocal accumulators 120, therefore, causing each of the localaccumulators to integrate twice. A resultant technical advantage of suchconfiguration, may be an overall reduction in mismatch due to higheraccuracy current values produced by each of the binary-weighted DACs ofthe segmented global reference generator.

Additionally, or alternatively, the system 100 may, in some embodiments,include a plurality of local analog-to-digital converters (ADCs) (notshown) that function to receive outputs from the output circuitry ofplurality of local accumulators 120. Specifically, in some embodiments,once a local accumulator 120 has achieved a sufficient (stored) chargevalue on a capacitor or the like, this charge value may be output ordefine an analog reference signal to a corresponding local ADC thatconverts an analog input signal to a binary output by comparing it tothe analog reference signal. In such embodiments, each local ADC mayinclude comparator circuitry that may be used to compare the analoginput signal to a reference signal for purposes of determining orgenerating the binary output, as described in U.S. patent applicationSer. No. 15/890,402, which is incorporated herein by this reference inits entirety.

Similar to the global DAC-to-local DACs architecture(s) describedherein, a global reference signal generator (e.g., a global ADC) tolocal ADCs architecture may be implemented. In such implementation, aplurality of local ADCs may be provided one or more reference signalsfrom a global ADC via a shared common signal path. Such configurationmay similarly achieve several technical benefits including a smallerarea of circuitry architecture, energy efficiencies (e.g., lower powerconsumption), and the like.

Referring to FIG. 1B, another implementation of a local accumulator 120is illustrated in which the global reference generator 110 functions togenerate bias voltages bias voltages (e.g., global reference signals)for an amplifier-based integrator of the local accumulator 120. Atechnical advantage of such implementation includes enabling the localaccumulator 120 with a single current source (rather than two currentsources). In a preferred configuration of the local accumulator 120 withan amplifier-based integrator, a dummy path may be implemented thatreduces an effect of charge injection, which occurs when (transistor)switches actuate to an ON or OFF state. Such a configuration may beachieved with an additional transistors.

Additionally, or alternatively, a gate of a bias n-channel MOSFET (nmos)or the like may be grounded (rather than being connected to a bias fromthe global reference generator 110). One or more drains of the switchesin this configuration of the local accumulator 120 may be connected inthe following manner: a drain of a left (replica) switch may beconnected to a drain of a right switch and a drain of a right (replica)switch may be connected to a drain of a left switch.

2. A Method for Mixed Signal Computing

As shown in FIG. 2 , the method 200 includes providing a global analogreference signal to be transmitted along a shared signal communicationpath S210, transmitting the global analog reference signal via theshared signal communication path S215, duplicating the global analogreference signal at each of a plurality of local accumulators S220, andgenerating at each of the plurality of local accumulators an outputsignal S230.

The method 200 functions to enable a global reference generator, such asa global DAC, to provide one or more global reference signals along ashared signal communication path. Along the shared signal communicationpath, the method 100 permits any local accumulators connected thereto,such as local DACs, to copy the one or more analog global referencesignals to generate a final output. Thus, in the method 100, for eachglobal DAC there may be multiple local DACs that rely on the global DACfor reference signals for the purpose of generating an output signal ateach of the multiple local DACs.

S210, which includes providing a reference signal to be transmittedalong a shared signal communication path, functions to use a digital(binary) input signal to generate an analog reference signal to aplurality of local accumulators. In one example, a binary or digitalsignal input may be received at a global DAC (e.g., global referencegenerator 110), that the global DAC translates into a global analogreference signal that may be propagated to each of a plurality of localDACs (e.g., local accumulators 120) via a shared signal communicationpath. The number of clock cycles over which the global analog referencesignal is transmitted to each of the plurality of local DACs may dependon a configuration (e.g., bit configuration and/or signal encodingscheme) of the global DAC.

In a first implementation, when the global DAC comprises abinary-weighted analog reference signal generator, the global DAC may beconfigured to generate one reference signal that is transmitted over Nclock cycles (e.g., binary summation over time). In such implementation,it may take up to N clock cycles (where N matches the N-bit of theglobal DAC) to transmit an analog reference signal sufficient togenerate an output signal at each of the local DACs. Additionally, oralternatively, a log(N)-bit global DAC may be employed when or if outputsignal levels are binary weighted. By way of an example, an 8-bit DACmay function to generate signal levels between 0-255, but for thepurposes of the global DAC, only signal levels 0, 1, 2, 4, 8, 16, 32,64, and 128 may be required. Thus, significantly reducing the signaloutput levels. That is only 8 output signal levels, even if the outputsignal levels are binary spaced (i.e., binary weighted output).

In a second implementation, when the global DAC comprises anon-binary-weighted analog reference signal generator, it may take up to2{circumflex over ( )}N cycles (N matches the N-bit of the global DAC)to transmit an analog reference signal sufficient to generate an outputsignal at each of the local DACs.

In a third implementation, the global DAC may be configured to generatean N-reference signal that is transmitted over a single cycle. In thisway, the output conversion time at the local DAC is significantlyreduced and the local DAC may be limited to performing additionfunctionality to an energy storage device, such as a capacitor.

In a fourth implementation, the global DAC may be configured to generatean M-reference signal over ceil (N/M) cycles. In this way, analogreference signals generated by the global DAC may be transmitted inpairs to each of the local DACs.

Additionally, various encodings schemes may be implemented via themethod 100 for achieving a final output signal at the local DACs. Forexample, one or more of thermometer encoding, binary encoding, segmentedencoding, logarithmic encoding, and the like may be implemented. In someembodiments, one or more of the various encoding schemes may beimplemented in combination in which various and/or a combination ofglobal DACs function to generate reference signals according to one ormore encoding types selected among various encoding schemes. In oneexample, in a system having at least two global DACs, where each of theat least two global DACs functions to provide reference signals to aplurality of local DACs associated therewith, a first of the two globalDACs may be designed to generate reference signals in accordance withthermometer encoding and a second of the at least two global DACs may bedesigned to generate reference signals using binary-weighted encoding.It shall be noted that the global DACs described herein may be capableof employing any known, combination, or reasonable encoding scheme.

Additionally, or alternatively, S210 may function to provide and/ortransmit the signals in any suitable manner including: using the globalDAC to provide multiple analog reference signals that remain constant orfixed; providing a single analog reference signal that varies or changesor over time (e.g., binary summation); providing multiple analog signalsthat vary over time, and the like.

In one implementation, S210 may function to implement a global referencegenerator having a pulse modulator or the like that enables a variationof a pulse width and/or a number of pulses generated per clock cycle.Accordingly, in one or more embodiments, S210 may function to increaseand/or decrease a pulse width during a clock cycle that enables a localaccumulator, such as a local DAC, to correspondingly, vary (increase ordecrease) a charge (voltage) stored on an energy storage device (such asa capacitor). Additionally, or alternatively, S210 may function toincrease and/or decrease a number of pulses during a clock cycle thatenables a local accumulator, such as a local DAC, to correspondingly,vary (increase or decrease) a charge (voltage) stored on an energystorage device (such as a capacitor).

Additionally, S215 may function to provide the reference signal over ashared or common signal communication path. In a preferred embodiment,the shared signal communication path originating at a global DAC mayextend to each of a plurality of local DACs thereby placing the globalDAC in operable signal communication with each of the plurality of localDACs. In this way, each reference signal generated by the global DAC maybe passed along to each of the plurality of local DACs along the sharedsignal path.

S220, which functions to duplicate the global analog reference signal,functions to copy the global analog reference signal transmitted alongthe shared signal communication path. Specifically, each of the localDACs may include current mirrors that when implemented by the local DACfunction to copy a global analog reference signal or charge (eithervoltage or current) provided by the global DAC.

Depending on encoding scheme or signal transmission method implementedat the global DAC, S220 functions to accumulate the global analogreference signal (or a resulting electrical charge) onto an energystorage device (e.g., a capacitor) at each of the local DACs that is insignal communication with the global DAC along the shared signalcommunication path. Specifically, S220 functions to add or subtractcharge from capacitors of the local accumulators. S220 may function toaccumulate or generate a charge in any suitable manner including usingcharge pump circuitry, using pulsed current sources, using anintegrating amplifier (e.g., an integrator).

In some embodiments, a manner in which each of the plurality of localDACs accumulates and/or integrates a charge on an energy storage deviceover a predetermined number of clock cycles is based on a receipt of oneor more bias input signals at each of the plurality of local DACs.Accordingly, S220 may additionally function to receive at each of theplurality of local DACs one or more bias input signals from a bias inputsource (e.g., a global bias input source or generator, etc.) thatindicates to a local DAC whether an electrical charge should beincremented to or decremented from a charge on an energy storage device(e.g., a capacitor or the like).

S230, which includes generating an output charge, functions to output asum or an accumulation of a charge based on one or more global analogreference signals from the global reference generator. In the case thatthe energy storage device of the local DAC (e.g., local accumulator)comprises a capacitor, S230 may function to output the resultant chargeof the capacitor in various manners.

In one implementation, S230 may function to connect the capacitor to anoutput destination (terminal) and output the summed or accumulatedcharge (current or voltage) of the capacitor directly to the outputdestination.

In a second implementation, S230 may function to connect the capacitorto an input terminal of a current source, such as a (flash) transistor,and output the charge on the capacitor to the input of the currentsource. Additionally, or alternatively, in a third implementation, S230may function to connect the capacitor to an input of a tunable resistorand output the charge of the capacitor to the input of the tunableresistor.

Additionally, or alternatively, in a further implementation, the analogsignal references from the global DACs may be used to performed a pulsedwrite of a non-volatile memory device, such as a resistive random accessmemory (RRAM). In such implementation, the output generated in S230 mayinclude a current signal or an impedance.

It shall be understood that the method 200 is an exemplary method thatmay be implemented in any suitable order to achieve the inventionsand/or embodiments of the inventions within the purview or that may beeasily contemplated in view of the disclosure provided herein. Thus, theorder and process steps should not be limited to the exemplary orderprovided herein.

The methods of the preferred embodiment and variations thereof can beembodied and/or implemented at least in part as a machine configured toreceive a computer-readable medium storing computer-readableinstructions. The instructions are preferably executed bycomputer-executable components preferably integrated with thelithography system and one or more portions of the processors and/or thecontrollers implemented thereby. The computer-readable medium can bestored on any suitable computer-readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component ispreferably a general or application specific processor, but any suitablededicated hardware or hardware/firmware combination device canalternatively or additionally execute the instructions.

Although omitted for conciseness, the preferred embodiments includeevery combination and permutation of the various methods, apparatus, andsystems described herein.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

What is claimed is:
 1. A mixed-signal integrated circuit comprising: areference signal source configured to generate a plurality of currentreference signals based on an input of digital data; a shared signalpath that is in electrical connection with an output terminal of thereference signal source, wherein the reference signal source isconfigured to output, via the output terminal, the analog referencesignals to the shared signal path; a plurality of current sourcesarranged in electrical connection along the shared signal path, whereineach of the plurality of current sources is configured to copy one ormore of the plurality of current reference signals; and a control signalsource configured to generate a control signal that informs a currentcopying operation of each of the plurality of current sources.
 2. Themixed-signal integrated circuit according to claim 1, wherein: each ofthe plurality of current sources comprises a current mirror, and each ofthe plurality of current sources is configured to implement the currentmirror to copy the one or more the plurality of current referencesignals.
 3. The mixed-signal integrated circuit according to claim 1,wherein each of the plurality of current sources comprises a pair ofcurrent mirrors, and each of the plurality of current sources isconfigured to implement the pair of current mirrors to copy the one ormore of the plurality of current references signals based on the controlsignal.
 4. The mix-signal integrated circuit according to claim 3,wherein the control signal comprises a differential signaling input thatcontrols the current copying operation of each of the plurality ofcurrent sources.
 5. The mixed-signal integrated circuit according toclaim 3, wherein each of the plurality of current sources comprises apair of current mirrors, and each of the plurality of current sources isconfigured to implement the pair of current mirrors to generate eitheran additive current or a subtractive current based on the controlsignal.
 6. The mixed-signal integrated circuit according to claim 1,wherein an output terminal of each of the plurality of current sourcesis electrically connected to one input terminal of a plurality of inputterminals of a neural network implementation, and one or more of theplurality of current sources is configured to output to a distinct oneinput terminal of the plurality of input terminals of the neural networkimplementation.
 7. The mixed-signal integrated circuit according toclaim 6, wherein: each of a plurality of output terminals of the neuralnetwork implementation is electrically connected to an input terminal ofeach of a plurality of analog-to-digital converters (ADCs), and each ofthe plurality of output terminals of the neural network implementationsources a sum of currents output from the plurality of current sourcesto a distinct one of the plurality of ADCs.
 8. The mixed-signalintegrated circuit according to claim 7, wherein each of the pluralityof ADCs outputs a distinct control signal to a respective one of theplurality of current sources.
 9. The mixed-signal integrated circuitaccording to claim 1, wherein: the reference signal source comprises anN-bit digital-to-analog converter configured to output N currentreference signals to the shared signal path, and N is greater than one(1).
 10. The mixed-signal integrated circuit according to claim 1,wherein: the reference signal source comprises a binary-weighteddigital-to-analog converter configured to generate binary-weightedcurrent signals based on the input of digital data, and the plurality ofcurrent reference signals comprises a plurality of binary-weightedcurrent signals that vary in value.
 11. The mixed-signal integratedcircuit according to claim 1, wherein the shared signal path comprises asingle electrically conductive signal wire having multiple connectionsthat connect each of the plurality of current sources at distinctpositions along the shared signal path.
 12. The mixed-signal integratedcircuit according to claim 1, wherein: the shared signal path comprisesa single electrically conductive signal wire having multiple connectionterminals that connect an input terminal of each of the plurality ofcurrent sources at distinct positions along the shared signal path, andeach of the plurality of current sources being serially arranged alongthe shared signal path downstream of the reference signal source.
 13. Anintegrated circuit comprising: a reference signal source configured togenerate analog reference signals based on an input of digital data; ashared signal path that is in electrical connection with an outputterminal of the reference signal source, wherein the reference signalsource is configured to output, via the output terminal, the analogreference signals to the shared signal path; a plurality of currentsources electrically arranged along the shared signal path, wherein eachof the plurality of current sources is configured to generate currentbased on the analog reference signals of the shared signal path; and abias signal source configured to generate a bias signal input thatinforms a current generation of each of the plurality of currentsources.
 13. An integrated circuit comprising: a reference signal sourceconfigured to generate analog reference signals based on an input ofdigital data; a shared signal path that is in electrical connection withan output terminal of the reference signal source, wherein the referencesignal source is configured to output, via the output terminal, theanalog reference signals to the shared signal path; a plurality ofcurrent sources electrically arranged along the shared signal path,wherein each of the plurality of current sources is configured togenerate current based on the analog reference signals of the sharedsignal path; and a bias signal source configured to generate a biassignal input that informs a current generation of each of the pluralityof current sources.
 14. The integrated circuit according to claim 13,wherein: each of the plurality of current sources comprises a currentmirror, and each of the plurality of current sources is configured toimplement the current mirror to copy the one or more the plurality ofcurrent reference signals.
 15. The integrated circuit according to claim13, wherein each of the plurality of current sources comprises a pair ofcurrent mirrors, and each of the plurality of current sources isconfigured to implement the pair of current mirrors to copy the one ormore of the plurality of current references signals based on the biassignal input.
 16. The mix-signal integrated circuit according to claim3, wherein the control signal comprises a differential signaling inputthat controls the current copying operation of each of the plurality ofcurrent sources.
 17. The mixed-signal integrated circuit according toclaim 3, wherein each of the plurality of current sources comprises apair of current mirrors, and each of the plurality of current sources isconfigured to implement the pair of current mirrors to generate eitheran additive current or a subtractive current based on the controlsignal.
 18. A method of implementing a mixed-signal computing circuit,the method comprising: sourcing, by a reference signal source, aplurality of analog reference signals along a shared signalcommunication path to a plurality of current sources, wherein: each ofthe plurality of current sources is serially arranged in electricalconnection with the shared signal communication path, and each of theplurality of current sources is configured to copy one or more of theplurality of analog reference signals; and implementing a control signalsource configured to generate a control signal that informs a currentcopying operation of each of the plurality of current sources.
 19. Theintegrated circuit according to claim 18, wherein: each of the pluralityof current sources comprises a current mirror, and each of the pluralityof current sources is configured to implement the current mirror to copythe one or more the plurality of analog reference signals.
 20. Theintegrated circuit according to claim 18, wherein each of the pluralityof current sources comprises a pair of current mirrors, and each of theplurality of current sources is configured to implement the pair ofcurrent mirrors to copy the one or more of the plurality of analogreferences signals based on the control signal.